The present invention relates to ball bearings, and to axially preloaded ball bearing assemblies supporting a rotating element.
Ball bearings are used to permit constrained relative motion between a rotational element and a stator element. Ball bearings are used, for example, in: turbines, jet engines, dentistry equipment, bicycles, and automobile axles. Ball bearings may be used in virtually every mechanical assembly that utilizes a part rotating inside a housing.
Conventional ball bearings include a plurality of balls arrayed inside an arcuate allow the balls to rotationally move relative to the surfaces. One exterior surface of the arcuate race interfaces with and is secured to a surface of the rotating element, and another exterior surface interfaces with and is engaged by an arcuate surface of the stator element.
The race is generally comprised of an outer race and an inner race. During installation of one of the more common ball bearing assemblies, the inner race is press fit to the rotating element. This press fit secures the assembled ball bearing to the rotating element. A radial clearance is used to slip the stator element over a portion of the rotating element and slide the stator element onto and over the exterior surface of the outer race. The radial clearance used in assembly is generally not eliminated by press fitting the outer race to the stator element after installation. Both races are generally not press fit because the ball bearings would be too stiff to survive impact in applications where impact forces are applied to the mechanical assembly. Stiff ball bearings are more likely to irreparably separate on impact, most likely irreparably damaging the assembly. Thus, to reduce the stiffness of the ball bearings, the outer race is not press fit, and the radial clearance is allowed to remain between the outer race and the stator element.
The remaining radial clearance, however, allows for relative movement between the surface of the stator element and the exterior surface of the outer race. This relative movement or “fronting problem” leads to increased wear and decreased part durability. The clearance also provides additional space between the rotating element and the stator element in which the rotating element may rotate eccentrically in. The greater the size of the eccentric rotation of the rotating element about its axis of rotation the greater the radial force generated by the rotating element. The larger radial force increases the radial load on the ball bearings, further increasing component wear.
Thus, there is a need for a ball bearing that is not too stiff, yet is capable of reducing or eliminating the remaining radial clearance between the surface of the ball bearing and the surface of the stator element.